1. Technical Field
The present invention relates generally to imaging devices and printers, and more specifically to an apparatus for conditioning the moisture content of printing media.
2. Background Art
Imaging devices generally consist of a printing system, for example an ink-jet, laser-printing, or photocopying system, and a media transfer system which moves media, usually paper, along a path. The paper path generally directs paper from a tray containing fresh unused paper, through the process steps of the printing system, and out of the imaging device. The paper path often involves complicated manipulation of the paper through tight spaces and around corners, and the paper must be moved precisely along this path in order to assure accurate image replication. With features such as double-sided copying or output collation, paper path accuracy becomes even more important.
The moisture content of the paper within the system is an important factor for correct operation of the media transfer system. Overly moist paper becomes limp and can more easily wrinkle, contributing significantly to the occurrence of misalignment, low-quality output, and time-consuming paper jams. Additionally, the heating elements present in thermal or toner-based printing systems tend to heat paper unevenly and cause overly moist paper to curl, exacerbating paper path accuracy problems and jamming. Excessive moisture in electronic systems can also cause corrosion, clumping of toner, and due to variations in absorption rates, decreased output quality. Thus, decreasing the moisture content in the paper prior to transfer through the system can increase print quality and decrease misalignment and jamming.
The process of electrostatic imaging, whether in an electrophotographic copier, a laser printer, or other similar imaging device, typically involves the light-directed distribution of electrostatic charge over the surface of a photoconductive roller. A developing device deposits toner particles on the photoconductive roller and the toner particles are in turn deposited as an image onto a sheet media. After the image is transferred to the sheet media, the media typically passes between a fuser roller and a pressure roller where the media and toner are heated and pressed bonding the image onto the media. All media contain moisture. When the media passes between the rollers, at least a portion of the moisture is heated and evaporates. The resulting vapor may be transported to the various systems of the imaging device having a potentially detrimental effect upon those systems.
Prior art approaches to achieving moisture content reduction in imaging devices include pre-heating the paper along the paper path to decrease moisture content. If done as a preliminary step along the paper path, heating the paper can cause curling and jamming. Heaters and blowers that run nearly full time consume excess energy and further complicate the paper path. If no moisture-management system is used, the imaging system may have to be operated in a humidity-controlled environment.
The environment in which a device operates, including the temperature and relative humidity of the working environment, may affect overall device performance and life cycle. There may be advantageous affect to device performance and life cycle by conditioning a sheet media for use in an imaging device and controlling the moisture content of the sheet media while stored for use in a paper tray or cassette. Therefore, it may be advantageous to provide a system for removing moisture from paper without complicating the path of paper through the imaging device. It may also be advantageous to provide an energy efficient moisture removal system. Additionally, it may be advantageous to provide a simple and cost-efficient system. Advantage may also be found in providing a system that dries paper without subjecting it to unnecessary curling.
The present invention is directed to a moisture-reducing paper tray. The paper tray includes a desiccant that absorbs moisture from the environment of the paper tray and consequently the paper supply. Desiccants include but are not limited to the compounds including silica gel, activated alumina and lithium chloride salt. A desiccant naturally attracts moisture from gases and liquids. As a result, the desiccant may become saturated as moisture is absorbed or collects in the desiccant material. In one embodiment of the invention, a used desiccant may be changed for a fresh desiccant when required. In an alternate embodiment of the invention, the moisture-reducing paper tray may include a drying mechanism for drying the desiccant thereby eliminating a need to replace the desiccant. The desiccant may be pre-packaged in a packaging film which permits the free transfer of ambient air past the desiccant. Alternately, the paper tray may be lined with a desiccant. In another embodiment of the invention, the desiccant is shaped in a solid form similar to that of the paper within the tray and may be placed below a stack of sheet media stored in the paper tray. In one embodiment of the invention, a paper tray includes a recess formed in the interior of the tray. A desiccant is placed in the recess of the tray. A panel including a plurality of apertures may be placed between the recess and the media and permits air to be passively or actively circulated past the media and the desiccant.
The present invention may also include a drying mechanism for periodically restoring the drying properties of the desiccant. Heating a desiccant permits the material to dry out allowing repeated use. In one embodiment of the invention, heat from a heat source is periodically directed through the paper tray to purge the desiccant of the moisture it has absorbed. In another embodiment of the invention, a vent fan forces air past a heat source and the desiccant purging accumulated moisture. The drying process may operate intermittently, and may be initiated manually, following a pre-selected number of image forming cycles or as a portion of a routine system check. Application of heat to the desiccant may be by means of forced air or by a radiant source. Another embodiment of the invention includes a humidity sensor that monitors the moisture content of the desiccant. The humidity sensor may activate the heat source and/or a fan or blower when the moisture level reaches a pre-selected limit.
Because moisture in the paper tray environment is controlled passively, that is, by control of ambient environmental humidity, and because moisture control occurs when the paper or other media is stored in a relatively heavy stack placed in the tray, curling may be less likely to occur. Controlling or reducing moisture levels in sheet media may decrease the tendency of feed mechanisms to jam. Controlling or reducing moisture levels in sheet media may also reduce humidity and moisture within the imaging device thereby improving device performance, print quality and life cycles.
The present invention consists of the parts hereinafter more fully described, illustrated in the accompanying drawings and more particularly pointed out in the appended claims, it being understood that changes may be made in the form, size, proportions and minor details of construction without departing from the spirit or sacrificing any of the advantages of the invention.